A novel polymer-based nanocomposite was fabricated to investigate its shielding properties against high-energy electron radiation for potential applications in space industry. Bismuth oxide (Bi2O3) nanoparticles and multi-walled carbon nanotubes (MWCNT) were added to poly (methyl methacrylate) (PMMA) to fabricate the nanocomposite. Radiation shielding efficiency of different samples, pure PMMA, PMMA/MWCNT, and PMMA/MWCNT/Bi2O3, was characterized and compared with aluminum (Al). The electron-beam attenuation characteristics show that PMMA/MWCNT/Bi2O3 nanocomposite was 37% lighter in comparison with Al at the same radiation shielding effectiveness in electron energy range of 9-20MeV. Furthermore, mechanical and thermal properties indicate that PMMA/MWCNT/Bi2O3 can achieve significantly improved tensile strength, initial decomposition temperature, and glass transition temperature over pure PMMA. The stabled thermal properties, chemical structures, and morphology of all materials before and after electron irradiation lead to excellent radiation resistance of PMMA and nanocomposite. In conclusion, the proposed nanocomposite is a promising material for high-energy, electron-beam shielding applications.